A motor has been conventionally proposed which is provided with a thrust pressurization part that pressurizes one end of a shaft in an axial direction for suppressing positional displacement of the shaft in the axial direction. A flat spring or a coil spring having a cylindrical shape is used as a pressurization means that is used in the thrust pressurization part. Since a coil spring having a cylindrical shape is provided with a relatively large pressurization (urging) force, a coil spring is used for obtaining a relatively high effect for preventing positional displacement of the shaft.
In Patent Literature 1, a structure is described in which, in a motor device using a coil spring having a cylindrical shape, a thrust pressurization part is accommodated in an inside of a lead screw (shaft). According to this structure, the dimension of the motor (total length of motor) in the axial direction of the shaft can be shortened as much as possible while sufficiently securing stability of the pressurization mechanism to the shaft.
In Patent Literature 2, a structure of a motor device is proposed in which an end part of a shaft is rotatably supported through a ball that is held by a bearing member and the bearing member is held in an opening part (through hole) in a state urged in an axial direction of the shaft by a coil spring for preventing positional displacement in the axial direction of the shaft. In other words, since the bearing member is held in the opening part in a slidable state in the axial direction, a clearance is formed between an outer peripheral face of the bearing member and an inner peripheral face of the opening part.
In Patent Literature 3, a motor device is described which is provided with a support part supporting an output side end part of a shaft that is protruded from an output side end face of a stator and, in which a shaft frame is fixed to the output side end face of the stator and a support part by which the output side end part of the shaft is supported is provided at a tip end of the shaft frame. The shaft is rotationally supported by a ball that is held by the support part. The support part is fixed to a hole that is formed at the tip end of the shaft frame. The shaft of the motor described in the former Patent Literatures is formed with a lead screw part. The lead screw part is normally engaged with a driven body referred to as a carriage or the like and the driven body is moved back and forth in the axial direction of the shaft.
[PTL 1] Japanese Patent Laid-Open No. Hei 8-280155
[PTL 2] Japanese Patent Laid-Open No. 2006-174595
However, in the structure described in Patent Literature 1, since the coil spring in a cylindrical shape is provided in the inside of the lead screw, workability is not satisfactory when the compression coil spring is to be accommodated in the inside of the lead screw. Further, since the coil spring is accommodated in the inside of the lead screw, a wire diameter and a distance between coil wires of the coil spring in a cylindrical shape are limited and thus a sufficient pressurization cannot be applied to the shaft.
In the structure described in Patent Literature 2, the clearance causes the following problems. In other words, when the bearing member is inclined within the opening part due to the clearance, the position of the ball held by the bearing member is varied and thus the shaft supported by the ball in an abutted state is inclined. In association with this matter, in designing the motor, a sufficient space is required between an outer peripheral face of a rotor and an inner peripheral face of a stator so that the rotor is not contacted with the stator (coil). Therefore, a main body portion (stator) of the motor is enlarged in the radial direction.
In the structure described in Patent Literature 2, for example, as shown in FIG. 7, if simply changed to a structure where the lead screw part is replaced with a pinion 92 and a rotational force of a motor 90 is outputted through a gear 94 which is engaged with the pinion 92, an external force is applied to the shaft in a direction perpendicular to the axial direction (pinion 92) and thus a shaft frame 96 may be deformed by the external force. As a result, the position of a support part 98 by which an end part 92a of the shaft is supported is displaced and thus an outer wall of the rotor and an inner wall of the stator may be interfered with each other. Further, in the worst case, the shaft may be disengaged from the support part 98 or the bearing member 98a structuring the support part 98 may be detached from a mounting hole 96a which is formed at the tip end of the shaft frame.
In view of the problems described above, it is desirable to provide a motor device which is capable of securing a satisfactory workability when a thrust pressurization part is to be arranged on an inner side of a rotor, securing a sufficient pressurization force by a coil spring to a shaft and, in addition, increasing a length in an axial direction of the shaft as much as possible.
It is further desirable to provide a motor device which prevents inclination of the shaft occurring with inclination of the bearing member to restrain increase of the motor size.
It is further desirable to provide a motor device in which, in a motor having a pinion with which a gear is engaged for transmitting a driving force from the motor to an output shaft, a trouble is prevented which occurs when an external force acts on the shaft in a direction perpendicular to the axial direction of the shaft.